Washington, DC—In a groundbreaking discovery, a team of astronomers led by Carnegie Science has found compelling evidence of an atmosphere surrounding a rocky exoplanet, TOI-561 b. This discovery, published in The Astrophysical Journal Letters, was made using NASA’s James Webb Space Telescope (JWST) and challenges existing theories about the atmospheric retention capabilities of ultra-hot, rocky planets.
TOI-561 b is a rocky planet with twice the mass of Earth, orbiting its host star at a mere fraction of the distance between Mercury and the Sun. Despite its extreme proximity, which results in a year lasting just 10.56 hours, the planet retains a thick atmosphere, a finding that defies previous expectations.
Unexpected Atmospheric Retention
The planet’s atmosphere was detected using the JWST’s Near-Infrared Spectrograph (NIRSpec), which measured the planet’s dayside temperature. The findings revealed a temperature significantly lower than expected for a bare rock, suggesting the presence of a substantial atmosphere.
“Based on what we know about other systems, astronomers would have predicted that a planet like this is too small and hot to retain its own atmosphere for long after formation,” explained Nicole Wallack, a Carnegie Science Postdoctoral Fellow and the paper’s second author. “But our observations suggest it is surrounded by a relatively thick blanket of gas, upending conventional wisdom about ultra-short-period planets.”
The Role of the Host Star and Planetary Composition
TOI-561 b’s host star is much older than our Sun, which may contribute to the planet’s ability to retain its atmosphere. The planet’s low density further supports the presence of an atmosphere, as noted by Johanna Teske, the paper’s lead author. “It’s not what we call a super-puff—or ‘cotton candy’ planet—but it is less dense than you would expect if it had an Earth-like composition,” she explained.
The planet’s composition, potentially formed in a different chemical environment, may also play a role. “TOI-561 b is distinct among ultra-short period planets in that it orbits a very old—twice as old as the Sun—iron-poor star in a region of the Milky Way known as the thick disk,” Teske noted. “It must have formed in a very different chemical environment from the planets in our own Solar System.”
Mechanisms Behind Atmospheric Stability
The research team explored several scenarios to explain the planet’s atmospheric retention. Anjali Piette, a co-author from the University of Birmingham, suggested that a thick volatile-rich atmosphere is necessary to account for the observations. “Strong winds would cool the dayside by transporting heat over to the nightside,” she said. “Gases like water vapor would absorb some wavelengths of near-infrared light emitted by the surface before they make it all the way up through the atmosphere.”
Tim Lichtenberg from the University of Groningen proposed that an equilibrium exists between the magma ocean and the atmosphere. “At the same time that gases are coming out of the planet to feed the atmosphere, the magma ocean is sucking them back into the interior,” he explained. “This planet must be much, much more volatile-rich than Earth to explain the observations. It’s really like a wet lava ball.”
Implications and Future Research
The discovery of an atmosphere on TOI-561 b opens new avenues for understanding planetary formation and evolution. These findings are part of the first results from JWST’s General Observers Program 3860, which involved continuous observation of the system for over 37 hours. The research team is now analyzing the full data set to further map the planet’s temperature and refine the understanding of its atmospheric composition.
The study represents a significant milestone in Carnegie Science’s long-standing tradition of excellence in planetary science. “These JWST powered breakthroughs tap directly into our long-standing strength in understanding how exoplanet characteristics are shaped by planetary evolution and dynamics,” said Michael Walter, Director of the Earth and Planets Laboratory.
As JWST continues to provide new insights into the cosmos, the scientific community eagerly anticipates further revelations about exoplanet atmospheres and their implications for our understanding of the universe.
